I created a snapshot, made some adjustments, then selected the snapshot, but it looked different than when I took it.Traced it to the ToneCurveEnable setting which was disabled when I took the snapshot, but enabled after selecting the snapshot further on down the road.Note: ToneCurveEnable setting is not in the develop settings when read by plugins/SDK either - I'm guessing there's a connection.This bug was logged a long time ago (against Lr3), but not fixed.Adobe: Please acknowledge this bug and fix in next release, OK?

I was told a day ago that I discovered a new bug and that it would be fixed in the next release. Here I find it's an issue at least five years old. Color me late to the party, but color Adobe later ;-) LRuserXY's point 2 above is a decent workaround. Crosspost: https://forums.adobe.com/message/9305841#9305841

I haven't had this problem before (or at least didn't notice it), however this problem still exists. I'm using the latest version of Lightroom Classic CC. Snapshots save everything except for the enabling preferences of the tone curve. If 'snapshot 2' is saved with disabled tone curve, once I click on another snapshot, clicking 'snapshot 2' results in a snapshot with all settings except disabled tone curve. My workaround is to update 'snapshot 2' with the disabled tone curve as the settings seem to stick even after switching snapshots. It's annoying, especially when I forget. This is 5 years old, but there are no other recent issues with this that I could find.

It goes further: syncing a tone curve across images will change the actual point curve, but will not sync the state of the toggle switch (on/off). Likewise, presets will not change the state of the tone curve's toggle switch either. This behavior is not typical. Any other panel (B&W, details, split toning, etc.) will sync the current visibility state AND the setting. Any other panel will save the adjustment AND the visibility state in presets as well.

The problem is annoying, to say the least, but I have made it 700+ times worse because I set a custom camera profile as a new camera default and import setting, but I didn't realize that the image I used to set the default had its tone curve toggled off. (It was before I realized that syncing images and presets weren't affecting the hidden tone curves, which is how I got into this mess in the first place.) And then I imported 700+ images and spent hours sorting, rating and adjusting the basic panel- exposure, wb, etc. Now that I have the images with correct exposures, I wanted to apply tone curves to give depth and contrast. And this is where I realized I had a problem. I expanded the tone curve panel and realized it was OFF and I can't sync or apply a preset to turn the darn thing "ON" for all of my images. Normally I could fix this is a few seconds by adjusting one image and syncing the rest to match it. All other panels' visibility state are saved in presets and sync correctly still. While I didn't want a tone curve in my default settings, I DO want to be able to apply a tone curve now and I am in quite bothered that I either have to manually turn them all on, or delete all the images and start over. UGGG.

Since the last 2 updates, images will not correctly sync, apply presets, and save/portray snapshots if the tone curve's visibility is being switched from on to off or from off to on. This has never been a problem before, and doesn't seem to affect any other develop panels (split tone, detail, color, etc.). In every other panel, ALL settings, including the toggle switch that affects the panel's visibility will sync. It doesn't matter if the visibility is being switched from on to off, or off to on.
To be clear about what I'm referring to when saying tone curve's visibility: I mean the little toggle switch in the top left of the tone curve panel. When hovering over the switch, Lightroom tool tips pops up with "turn on/off tone curve adjustments." The history panel records changes to this switch as "Enable Tone Curve Yes/No".

Try syncing 2 images with settings from any other panel, and the adjustments will sync AND the visibility state of the adjustment panel (toggled on or off).

PRESETS:

Same problem with presets. For the tone curve panel: adjustments are updated acording to the preset, but NOT the panel visibility. Presets affecting any other panel will update adjustments AND the visibility state (toggle on/off) according to how the preset was saved.

SNAPSHOTS:

Snapshots are finicky again with regard to Tone Curve visibility. If the snapshot is of the tone curve visibility toggled off, it will not save it that way initially. However, UPDATING an existing snapshot with current settings will get the snapshot to display a toggled off tone curve and it will switch back and forth accurately afterwards. Every other panel's visibility will stick upon creating a snapshot and doesn't need to be updated.

This hasn't always been a problem. And I recently set a new custom camera profile as the new camera default, without realizing that there was a hidden tone curve in the settings. Now I have 700 images that were imported with a tone curve toggled off and I can't undo it with a preset or by syncing. All I can think of is to manually toggle each switch back on. UGGG. If I had caught it earlier, I would have just reimported them, but I already started adjustments before I figured out that Lightroom wasn't working the way it did before the update, and I'm not sure what will take longer...

I recently changed my camera defaults to include a new custom profile for my 5d Mark iv images and what I thought were zeroed out settings. However, I didn't realize that the image I used when setting the new default had a hidden (disabled/toggled off) Tone Curve. And then I imported 700+ images and started adjusting them for hours. I actually wanted the tone curve to be linear in my default, so that I could adjust the images as needed with a tone curve, and as such it's not necessarily ruining my pictures by being off. The problem is that I'd like to add a tone curve now, but all the sudden I am not able to fix it the way I normally would (before the last 2 updates). Normally I would just turn the Tone Curve ON for one image and sync the rest of them to that. But syncing and presets aren't working for Tone Curve's visibility state (on/off). They apply an image's settings or the settings of a preset (change the tone curve, for example to medium contrast), but they are NOT changing the settings for the tone curve visibility (toggling the on/off switch). EVERY OTHER PANEL syncs both the adjustment AND the on/off state of the adjustment based on the preset or the image doing the syncing. But not the tone curve. And, of course, right now. It sounds ironic that I'd have this problem right when it stops working, but it's because of this not syncing issue that I'm in this boat and didn't realize my image still HAD a hidden tone curve and wasn't synced back to linear.

The Tone curve visibility problem continues to snapshots not saving correctly when the tone curve was in the "OFF" state, but I found a workaround for that and it wouldn't have helped me get out of this mess. (FYI, workaround is just updating the snapshot with the correct (off) settings again and the off state will stick).

If I hadn't spent so much time sorting through, rating, adjusting exposure, wb, and etc., I'd probably think it was faster just to delete them all and reimport them. All I can think of doing is to manually go through and switch the tone curve to "on" and then I'd be able to apply the necessary tone curve and be able to sync it again. But that's a pain and someone may have figured out a better way. If not, it definitely needs to be fixed, so if anything maybe this will enlighten someone who can fix it.